In resin vehicle parts each configured such that a reinforcing rib is provided standing on an inner surface of a panel body having a design surface, generally, a portion provided with the reinforcing rib vertically standing tends to have a high heat capacity per unit area. Accordingly, there is a problem that sink is liable to occur in an outer surface of the portion provided with the standing reinforcing rib in the panel body in association with thermal shrinkage or contraction of molten resin (hereinafter, also referred to as “resin shrinkage”) during injection molding. Therefore, study has been made on a structure that the wall thickness of a base end portion of the reinforcing rib is made thin to reduce the heat capacity and thereby reduce the sink and also the wall thickness of a leading end portion of the reinforcing rib is made thick to enhance the rigidity of the resin vehicle part.
For instance, Patent Document 1 discloses a resin exterior part for vehicle including a main body (corresponding to a panel body) forming the surface of a vehicle and a reinforcing rib extending in a planar direction on a back surface of the main body and protruding for reinforcing the main body. In this resin exterior part, the reinforcing rib is provided with a hollowed section in a base end portion corresponding to a root of the rib, thereby reducing the wall thickness thereof, and the reinforcing rib has an inclined shape inclining in a rib extending direction. According to this resin exterior part for vehicle, even when the hollowed portion is provided in the reinforcing rib to prevent the occurrence of sink in the outer surface of the main body, the reinforcing rib having the inclined shape oblique with respect to the rib extending direction can be prevented from falling, so that the rigidity of the resin exterior part for vehicle can be ensured.
Furthermore, Patent Document 2 discloses a molding method of an injection molded part in which a reinforcing rib is formed inside a corner section defined by two intersecting surfaces of a product. In this method, the wall thickness of the reinforcing rib is set thin to control a flow velocity of resin allowed to flow in the reinforcing rib, so that weld lines are not generated in a visible surface of the product.